Threading question

[Black Forest]

I finally understand why my threading tools are able to tip. This allows for the helix angle relief. But do I then grind the top of the tool to be flat inline with the through axis of the work? Meaning parrallel to the lathe ways.

Or do I leave it at the tippied angle? It seems to me that then the included angle of the cutting tool would not be correct....

Confused in the Black Forest!

The first picture is looking from the top down.
The second picture is looking at eye level to the back of the cutting tool.

[Highpower]

http://www.practicalmachinist.com/vb...set-up-238756/

1 Yes
1 No

Flip a coin?

[big job]

If I understand the ? correctly It will depend on the tool holder. If
the holder has a built in rake I think its 16.5* then you will have to
grind the top flat. Holders with no rake you leave it flat. At least
thats what I do. Not being good with words, my order of steps are
for a new tool blank
1-determine if the holder has a rake then grind the top flat if not
leave it alone
2-now grind the sides to 29* or whatever
3-I usually grind a slight radius on the cutting tip slightly
generally most common on Lantern style tool holders have rake
most quick change holders hold the tool flat. sam hope this helps

[Black Forest]

The cutter is presented with the top flat.

[Black Forest]

The bottome tool holder is the one I am asking about.

[JCHannum]

Theoretically, yes, you should grind the top to produce the perfect thread profile.

In actuality, any error will be so minimal that it would take far more inspection equipment than any HSM has available to identify it. As long as the threads produced are presentable and functional, there are many other things to worry about.

I use the Aloris threading tool discussed in the PM thread in a home made BXA sized holder. This is similar to your threading tool and is adjustable for side clearance angle also. When sharpening, I do it with the cutter in the holder on my T&C grinder, just skimming the top. This sharpens it as well as grinds the top to the preset angle. I don't get too hung up over the side angle. It can be set with a protractor, but unless very coarse threads are being cut, I just kind of eyeball it. You do want to remember to change it for RH vs LH threads.

These cutters are great, and reasonably priced. The holders are easily enough made in the shop if the price is unacceptable. The 60* threading blades come in three sizes for 4, 6 and 10 or more TPI and are large enough to last a lifetime with proper care.

[Black_Moons]

Yes, you change the angle some when you tilt it.
No, it does not likey matter enough to notice.

Yes, the top now has side rake.
No, a little side rake won't hurt anything.

If you really care, you should get one of those insert holders that has 'toping' inserts, one for each pitch basicly.

Personaly, I just use square HSS bits I ground into threading bits, and just grind lots of side relief to take care of the helix angle.

[Black Forest]

I have all the threading inserts for all the different pitches I use.

But I also have these very cool retractable threading tool holders. Makes it very fast and very easy to thread. The threads I am getting are fine and look good. I just wanted to know if I really wanted them correct if I should flatten the top of the cutting tool.

[philbur]

Trouble is once you've laid hands on more than $1,500 worth of threading toolholders (when new) cutting tool angles that were good enough aren’t …. well .... good enough.

Phil

[justanengineer]

Whether or not to flatten the top of the tool (aka rake angle) is a matter of preference, and is entirely situational, just as "pushing vs dragging" when doing conventional turning. I almost always "drag" the bit when turning, and also use a negative (tipped down into the thread) rake angle for threading as I find it a bit easier on the tool. Contrary to what some on here have or will say, its entirely personal opinion, and many professionals do it both ways. To support this to the naysayers, many carbide manufacturers recommend negative rake and dragging, and many carbide holders are manufactured this way.

As to your other question about the angle of the tool bit relative to the ways, it should always be perpendicular to the ways when threading, not at an angle as shown in your second 3d model.